Optical characteristics of (NH4)2SbF5 crystal at different phases

Spectra of principal refractive indices and birefringence in the range of transparency (1.5-4.5 eV) and spectra of the edge fundamental absorption (⋐ 5 eV) for (NH 4 ) 2 SbF 5 crystal were measured at different temperatures in the 78-300 K range, on the basis of which correspondent fundamental absorption spectra in the 5-20 eV range were calculated. On the basis of precise temperature measurements of sample optical thickness an availability of second order phase transitions at T e1 = 292 K and T e2 = 168 K was confirmed. Rapid temperature changes of optical thickness in the 120-158 K range were interpreted as diffused first order phase transition.